1. Field of the Invention
The present invention relates to improved high temperature, low residue viscous ell treating fluids and methods of using the fluids for treating subterranean zones.
2. Description of the Prior Art
High viscosity aqueous cross-linked gels are used in a variety of operations and treatments carried out in oil and gas wells. Such operations and treatments include, but are not limited to, production stimulation treatments, well completion operations, fluid loss control treatments and treatments to reduce water production.
An example of a production stimulation treatment utilizing a high viscosity cross-linked gelled fluid is hydraulic fracturing. In hydraulic fracturing treatments, the high viscosity fluid is utilized as a fracturing fluid and a carrier fluid for particulate propping agent, e.g., sand. That is, the high viscosity fluid is pumped through the well bore into a subterranean zone to be fractured at a rate and pressure such that fractures are formed and extended in the zone. Propping agent is suspended in the fracturing fluid so that the propping agent is deposited in the fractures. The fracturing fluid is then broken into a thin fluid and returned to the surface. The propping agent functions to prevent the fractures from closing whereby conductive channels are formed through which produced fluids can flow to the well bore.
A variety of cross-linking compounds and compositions have heretofore been utilized for cross-linking gelled aqueous well treating fluids. Various sources of borate have been utilized including boric acid, borax, sodium tetraborate, slightly water soluble borates such as ulexite, and other proprietary borate compositions such as polymeric borate compounds. Various compounds that are capable of releasing multivalent metal cations when dissolved in aqueous well treating fluids have also been used heretofore for cross-linking gelled aqueous well treating fluids. Examples of the multivalent metal ions are chromium, zirconium, antimony, titanium, iron, zinc and aluminum.
Delayed cross-linking compositions have also been utilized heretofore such as compositions containing borate ion producing compounds, chelated multivalent metal cations or mixtures of organotitanate compounds and polyhydroxyl containing compounds such as glycerol. However, high viscosity aqueous gels cross-linked with the above described cross-linking agents and compositions have encountered operational problems. That is, the high viscosity cross-linked gelled aqueous well treating fluids have often been difficult to break after being placed in a subterranean zone and upon breaking, leave residue in the subterranean zone, both of which interfere with the flow of produced fluids from the treated zone. Further, at high subterranean zone temperatures in the range of from about 125.degree. F. to about 350.degree. F., a relatively large quantity of gelling agent is required in the cross-linked gelled aqueous well treating fluid to achieve adequate viscosity which produces a greater amount of residue in the treated zone and the high viscosity produced rapidly declines with time.
Thus, there are needs for improved high temperature well treating fluids and methods of using such fluids wherein the fluids require less gelling agent thereby reducing the residue left in subterranean zones treated therewith and the treating fluids have high viscosities which are stable over time at high temperatures.